Terrestrial water storage changes of Qinghai Lake on the Tibetan Plateau from joint inversion of GNSS and InSAR data

While geodetic observations are now commonly used to retrieve terrestrial water storage changes at regional or watershed scales, their application at the local scale, such as individual lakes, remains limited due to spatial resolution constraints and the lack of onsite observations, especially in remote areas. This study investigated the deformation field and water storage changes at Qinghai Lake, China from January 2016 to December 2022 by integrating data from five Global Navigation Satellite System (GNSS) stations and Interferometric Synthetic Aperture Radar (InSAR) images. We observed that the area surrounding Qinghai Lake exhibited an overall subsidence trend with rates ranging from -2.89 to -0.30 mm/yr between January 2016 and August 2019. However, from September 2019 to December 2022, this trend reversed to an uplift with rates ranging from 2.20 to 4.89 mm/yr. This shift in deformation direction is largely attributed to changed precipitation influenced by large-scale atmospheric circulation. Furthermore, independent component (IC) analysis of the deformation field shows that the first two ICs accounted for 77.36% and 16.67% of the data variance, representing loading signals due to regional background hydrological loading and lake water storage gains, respectively. We then reconstructed the loading deformation associated with lake dynamics and inverted the lake water storage changes, which demonstrated high consistency (r=0.86) with lake volume changes estimated from satellite water level measurements, indicating that increases in lake surface water constitute a significant portion of the water storage increases.